1. Field of the Invention
The invention relates to a method of manufacturing transformer windings embedded in casting resin and, more particularly, to such transformer windings embedded in casting resin by winding coils respectively by themselves and independently of one another for disposition thereof in tandem in axial direction of the winding; placing the wound coils in a substantially annular casting mold having an inner and an outer jacket, with respective impregnated corrugated mats of insulating material as spacers disposed between the inner jacket and the coils as well as between the coils and the outer jacket, the inner and the outer jackets being fixed between mold end walls at respective ends of the casting mold; disposing the casting mold containing the wound coils in an evacuated chamber and pouring casting resin into the casting mold through an axially parallel slot formed in the outer jacket thereof; and permitting the casting resin to harden at least partly in the mold at elevated temperatures and at a pressure at least equal to atmospheric pressure.
With increasing use of casting resin transformers, the optimization, especially, of the casting resin which is used becomes increasingly important economically. For this reason, equally good utilization of the advantageous electrical and mechanical properties of the casting resin plastic is sought after, possibly smaller wall thicknesses of the casting resin body additionally offering considerable thermal advantages.
2. Description of the Prior Art
From European Patent Application No. 80 108 131, published July 8, 1981, a method of manufacturing windings for electrical equipment, the windings being embedded in casting resin, has become known heretofore, according to which, impregnated corrugated mats formed of insulating material serve as spacers for fixing the electrical equipment parts to be encapsulated in the casting mold. These mats of insulating material, which remain in the cast-resin body, simultaneously act as reinforcement for the casting resin plastic material, which increases the mechanical load-carrying capacity of the casting-resin plastic material.
By the aforementioned heretofore known method, windings of coils arranged in tandem in axial direction are also encased by casting, the casting being effected preferably with a mold disposed in a horizontal position in an evacuated chamber, the casting resin compound being through a slot extending parallel to the axis and formed in the outer surface of the casting mold, and the casting resin compound being permitted to set at least partly in the mold itself at elevated temperature and at atmospheric or higher pressure.
To perform the heretofore known method, however, spacers and reinforcement inserts, respectively, in very large numbers and with different dimensions are required, in turn, necessitating the provision of a multiplicity of expensive auxiliary tools for manufacturing them. For practical purposes, only spacers with specific dimensions graduated stepwise are made in order to limit the number of the auxiliary tools required for manufacturing the spacers, so that the electrical and the mechanical load-carrying capacity of the casting resin bodies is frequently not fully utilized.